Skinny tires, a heavy load of shagbark hickory, and a soft yard will do this. Here's another angle There's a cherry chunk or 2 in this load as well. The second load was mostly a dead dry elm, the few remaining hickory huge rounds, and the last of the big cherry. The elm was about 20" in diameter. This was the hickory I cut down in January. I got about a cord hauled out of the woods today. Now I gotta split it up. Which may happen about Easter. It looks like my cutting buddy is going to buy the old splitter he borrows.
It was down to the axle of the trailer. No problems with the Audi sinking with much wider tires. We unloaded it right there, then had to carry the rounds over 15 ft to the pile. The second load, we avoided the mushy part of the yard.
This was at my buddy's house, about a mile from my parents wood lot. He told me where to drive, just following orders. He wasn't mad, just surprised at the sinkage. Just driving my car back and forth over the ruts smoothed them out pretty good.